Quite simply, one of the greatest DW serials ever. Its virtually flawless and thoroughly enjoyable.
Tom and Lis are at the top of their form and the guest cast, most notably Bernard Archard and Michael Sheard are outstanding. The production design, special effects, costumes, and music are all top-notch. The story itself drips with the gothic horror themes that producer Philip Hinchcliffe and script editor Robert Holmes were fond of doing, with The Mummy movies used in this case with a sci-fi twist, making it quintessentially Doctor Who.
Every DW fan should watch this one. Its perfect.